A quick fastening device is a mechanical assembly comprising two portions, one of which is attached to the tool, a bucket for example, and the other one of which is borne by the arm of the machine.
The state of the art in this field is comprised, in particular, of the quick fastening device described in the French Patent published under No. 2809779.
The fastening device described in this patent comprises two substantially stirrup-shaped portions, the first portion, affixed to the arm of the machine, having a cradle that can be inserted under a shaft borne by the second portion, affixed to the tool.
The median portion of the second portion has a hook-shaped extension that can pass through an opening of the first portion and an opening of a locking plate sliding on the median portion of said first portion under the action of return springs.
Means are provided for maintaining the locking plate in the “set position”, that is to say, a position in which the hook-shaped extension can pass freely through the median portion of the first portion and the locking plate.
While passing through the two openings, the hook-shaped extension releases the locking plate which, under the action of the springs, is inserted under the extension.
As the surfaces (hook and plate) adapted to cooperate are more or less embedded in the ground, the plate is not completed inserted under the hook, thereby giving the illusion of a locking which, in fact, is incomplete.
As a result, shocks and vibrations can cause the tool that is incompletely connected to the arm of the machine to separate and drop during operation.
To overcome this disadvantage, it has been provided to equip the hook with at least one lateral lug that can pass through a notch provided on the opening of the first portion and on the opening of the locking plate. Therefore, passing through the two openings is possible only when the locking plate is in the set position.
As soon as the locking plate starts to be inserted under the hook, under the action of the springs, the aforementioned lug extends above the locking plate, opposing the pivoting of the second portion.
This safety device is particularly efficient, but it is dependent upon the action of the springs that oppose the backward movement of the locking plate.
If the springs break or are detached, there is nothing left to oppose the backward movement of the locking plate; such backward movement being facilitated when the locking plate is in a substantially vertical position, as it then slides downward, under its own weight, to occupy a position in which the notches and openings mentioned hereinabove coincide with one another: separation of the tool is possible.